This invention relates to plunger assemblies for applying pressure to provide intimate contact between two smooth layers of a material and in one aspect to such assemblies in a device for forming graphics via a transfer of material between the layers of the material.
U.S. Pat. No. 3,914,755 (the content thereof is incorporated herein by reference) describes a device for forming graphics along a two layer strip of radiation sensitive material via a transfer of material between the layers. The device comprises means for defining an exposure station including a plate mounted on a frame for the device which plate is essentially transparent to radiant energy. A path for the strip is defined through the exposure station adjacent one surface of the plate. A portion of a template is disposed between the plate and the strip which template portion has areas which are opaque to radiant energy and radiation transmissive areas corresponding in shape to a graphic to be formed. The strip material is exposed to radiation through the plate and template via a xenon flash lamp to form the graphic via adhesive contact between portions of the layers. Means are provided for bringing the layers of the strip material into intimate contact during exposure by the lamp which includes a plunger assembly for pressing the layers against the template and the plate. The plunger assembly comprises a soft flexible resilient pad providing a pressure surface for contacting the strip and a rigid member supporting the resilient pad on its side opposite the pressure surface. The plunger assembly is mounted on the frame for movement between a released position with the pressure surface of the pad spaced from the plate to afford movement of the strip material along the path, and an engaged position (to which engaged position the plunger assembly is moved when the strip material is exposed) at which the pressure surface of the pad presses the template and strip against the plate at the exposure station.
The pressure surface on the pad in the device described in U.S. Pat. No. 3,914,775, however, is planar, and thus the entire pressure surface comes into contact with the strip material at about the same time. The plunger assembly is moved quickly to its engage position so that such contact by the pressure surface tends to trap air between the layers of the strip material. Since formation of graphics by the device depends on intimate contact and an adhesive transfer of material between the layers in irradiated areas, air trapped between the layers can cause defects in the graphics formed, thus producing graphics of lesser precision than might otherwise be produced.